和大神们学习每天一题(leetcode)-Best Time to Buy and Sell Stock II

Say you have an array for which the ith element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times). However, you may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

本题主要在于判断当前价格是增加还是减少趋势

功能测试用例：{ 1,4,11,1,9}

特殊输入测试用例：NULL, {1},{1,2,3,4,5},{5,4,3,2,1}

class Solution{public:int maxProfit(vector<int> &prices){if (prices.size() < 2)//如果价格个数小于2则返回空return NULL;bool bFlag = false;//标记前一次比较是增还是减int  nMaxPro = 0, nLower = prices[0], nUpper = prices[0];//初始化最高和最低值为第一天的价格for (int nTemp = 0; nTemp < prices.size() - 1; nTemp++){if (prices[nTemp] <= prices[nTemp + 1])//判断价格是否上升{nUpper = prices[nTemp + 1];//将最高值赋为当前值if (bFlag == false)bFlag = true;}else//价格下降或不变{if (bFlag){nMaxPro += nUpper - nLower;bFlag = false;}nLower = prices[nTemp + 1];}}if (bFlag){nMaxPro += prices[prices.size() - 1] - nLower;}return nMaxPro;}};